A chemical attack on history
The Etruscan necropolises at Tarquinia hold some of the most significant pre-Roman paintings in the Mediterranean. These bright frescoes, dating from the 7th to the 3rd centuries BCE, are under a slow, persistent chemical attack. The tombs are subterranean chambers, or hypogea, carved directly into the local volcanic tuff, a porous rock. This geology is important to both their preservation and their current decay.
Modern agriculture in the surrounding region uses nitrogen-based fertilizers. Rainwater carries these chemicals from the fields into the soil, altering the local groundwater chemistry. As this slightly more acidic water percolates through the porous tuff, it dissolves calcium carbonate (calcite) from the rock matrix. Inside the tombs, this calcite-rich water seeps through the walls and evaporates, depositing a hard, opaque crust of recrystallized calcite on the fresco surfaces. This process, which obscures and damages the ancient pigments, has been measured to proceed at a rate of 0.1 millimeters per year. Other studies have identified that certain bacteria, such as Bacillus species that survive biocide treatments, can also be responsible for producing these damaging calcium carbonate layers.